1. Field of the Invention
The present invention relates to vapor recovery systems for vehicles and, more particularly, to onboard refueling vapor recovery system using an electronic control valve and a method for operating the electronic control valve.
2. Discussion
Increasingly stringent environmental standards have resulted in the passage of regulations which necessitate a significant reduction in fuel vapors escaping from a vehicle fuel tank during refueling. These regulations generally strive to essentially eliminate fuel vapor escaping to the atmosphere during refueling. The resultant emission control systems are referred to as onboard refueling vapor recovery (ORVR) systems. In an ORVR system, the filler neck of the fuel system is designed to a diameter to create a liquid seal in the filler neck to prevent vapors from escaping from the fuel tank through the filler neck. During refueling, the fuel volume within the tank increases, thereby reducing the available space for fuel vapors. The pressure created by filling the tank causes the fuel vapors to exit through an exhaust port to a fuel vapor canister. The fuel vapor canister typically includes a charcoal element to capture hydrocarbons while releasing filtered vapors into the atmosphere.
In a typical ORVR system, a control valve is placed in the vapor transmission path between the fuel tank and the canister. The primary purpose of the control valve is to enable the transmission of vapor while preventing the transmission of liquid fuel to the collection canister. If liquid fuel reaches the canister, a situation referred to as carryover, fuel can collect within the canister. Because the canister may later be purged to provide fuel to the vehicle via the intake manifold, excessive fuel carryover may cause liquid fuel to exit the fuel system or interfere with engine operation.
Existing ORVR control valves are mechanical valves which are normally open, providing a vapor path between the fuel tank and the canister. However, these normally open valves must be adaptable to close off the vapor path between the fuel tank and the canister during conditions such as vibration, slosh, and vehicle tilting which might otherwise result in a carryover condition. Typical valves include a buoyant member with a bias toward an open position. The valve is responsive to slosh, vibration, and tilting conditions to close the vapor passage. However, such valves are often slow to respond and include many moving parts which eventually deteriorate, thereby adversely affecting operation of the refueling valve.
Thus, it is an object of the present invention to provide an onboard refueling vapor recovery system having an electronic control valve to selectively enable the passage of fuel vapor from the fuel tank to the canister during predetermined conditions.
It is a further object of the present invention to provide an onboard refueling vapor recovery system having an electronic control valve which is generally closed to prevent liquid fuel from traveling to the canister, except during refueling when the electronic control valve is opened.
It is yet a further object of the present invention to provide an onboard refueling vapor recovery system having an electronic control valve and a method for controlling the electronic control valve which enables vapor to pass from the fuel tank to the canister only during predetermined conditions.
It is yet a further object of the present invention to provide a method for controlling an onboard refueling vapor recovery system having an electronic control valve, where the method prevents liquid fuel from traveling to the canister.